For photomultiplier tubes used in high-temperature, high-vibration environments, as in oil exploration, noise due to vibrations and degradation over time are problems, since accurate operations are required while drilling deep underground. The electrode in the photomultiplier tube must be securely and fixedly supported, since noise generated during vibrations is caused mainly by displacement of the electrode within the photomultiplier tube.
When forming an electron multiplying portion in a conventional photomultiplier tube, wherein dynodes of a plurality of stages are inserted into and supported by two ceramic base plates, individual support portions are formed on either end of each dynode, and corresponding individual linear portionslits are formed in each ceramic base plate. The support portions are supported through insertion into the corresponding slits.
A photomultiplier tube disclosed in Japanese unexamined patent application publication No. HEI-9-180670 is provided with two support portions protruding one from each end of the second and third dynodes. More specifically, these dynodes are configured from a concave plate part, forming the secondary electron emitting surface, and two upper and lower support plate parts extending from the top and bottom ends of the concave plate part toward the back side thereof. Support portions are formed on both ends of each of the top and bottom support plate parts. Holes are formed in each of two ceramic base plates for engaging the support portions on the two dynodes. Each support portion is supported by inserting the support portions into the corresponding holes and sandwiching each dynode between the two ceramic base plates.
Further, in a photomultiplier tube disclosed in Japanese unexamined patent application publications Nos. SHO-60-262340, SHO-60-254547, and SHO-60-254548, two support portions are formed on both ends of each dynode, extending along the same plane. A single slit corresponding to the two support portions on each dynode is formed in the two base plates. The two support portions are fixed in the base plates by inserting the support portions into the corresponding single slit and bending over the ends of the support portions.
However, when supporting each end of a dynode with a single support portion, rattling tends to occur in the direction of rotation about the support portions. Such movement by the dynodes can affect the output signals.
In the photomultiplier tube of Japanese unexamined patent application publication No. HEI 9-180670, if clearance is provided to enable the dynodes to be easily inserted into the holes, the plate-shaped concave plate portions and the top and bottom support plate portions deform when exposed to severe vibrations, causing the dynodes to rattle severely in the holes. Hence, the dynodes cannot be reliably fixed.
In the photomultiplier tube according to Japanese unexamined patent application publications Nos. SHO-60-262340, SHO-60-254547, and SHO-60-254548, if clearance is provided to enable the dynodes to be easily inserted into the slits, then the dynodes rattle severely in the lengthwise direction of the slits. Hence, the dynodes cannot be reliably fixed.
In view of the foregoing, it is an object of the present invention to provide a photomultiplier tube with good vibration characteristics whose parts can be fixed solidly to prevent rattling between the dynodes and the base plates.